What is the magnitude of the frictional force present if a 3kg mass being pulled by a horizontal force of 5 newtons towards the right experiences an acceleration of -0.33 m/sec^2?
5 - friction force = m a = - 3 * .33 = - 0.99
so
friction force = 5 + 0.99 = 5.99
note it is de accelerating so the friction is more than the pull